Content deleted Content added
MalnadachBot (talk | contribs) m Fixed Lint errors - replaced obsolete center tags. (Task 12) |
Citation bot (talk | contribs) Add: journal, isbn. | Use this bot. Report bugs. | Suggested by Abductive | #UCB_webform 2844/3849 |
||
Line 1:
'''Oxidation with chromium(VI) complexes''' involves the conversion of alcohols to carbonyl compounds or more highly oxidized products through the action of molecular chromium(VI) oxides and salts.<ref>{{cite journal|author=Luzzio, F. A.|journal=[[Org. React.]]|title=The Oxidation of Alcohols by Modified Oxochromium(VI)–Amine Reagents|year=1998|volume=53|page=1|doi=10.1002/0471264180.or053.01|isbn=0471264180 }}</ref> The principal reagents are Collins reagent, PDC, and PCC. These reagents represent improvements over inorganic chromium(VI) reagents such as [[Jones reagent]].
==Inventory of Cr(VI)-pyridine and pyridinium reagents==
Line 5:
One family of reagents employs the complex CrO<sub>3</sub>(pyridine)<sub>2</sub>.<ref>{{cite book |doi=10.1007/0-387-25725-X_1|chapter=Chromium-based Reagents|title=Oxidation of Alcohols to Aldehydes and Ketones|series=Basic Reactions in Organic Synthesis|year=2006|pages=1–95|isbn=0-387-23607-4}}</ref>
*[[Sarett oxidation|Sarett's reagent]]: a solution of CrO<sub>3</sub>(pyridine)<sub>2</sub> in pyridine. It was popularized for selective oxidation of primary and secondary alcohols to carbonyl compounds.
*[[Collins reagent]] is a solution of the same CrO<sub>3</sub>(pyridine)<sub>2</sub> but in dichloromethane. The Ratcliffe variant of Collins reagent relates to details of the preparation of this solution, i.e., the addition of chromium trioxide to a solution of pyridine in methylene chloride.<ref name=JCC>{{cite journal | author = J. C. Collins, W.W. Hess | title = Aldehydes from Primary Alcohols by Oxidation with Chromium Trioxide: Heptanal | journal = Organic Syntheses | volume = 52 | pages = 5 | doi = 10.15227/orgsyn.052.0005 | year = 1972}}</ref>
The second family of reagents are ''salts'', featuring the pyridinium cation (C<sub>5</sub>H<sub>5</sub>NH<sup>+</sup>).
Line 38:
==Comparison with other methods==
Methods employing dimethyl sulfoxide (the [[Swern oxidation|Swern]] and [[Moffatt oxidation]]s) are superior to chromium(VI)-amines for oxidations of substrates with heteroatom functionality that may coordinate to chromium.<ref>Tidwell, T. ''Org. React.'' '''1990''', ''39'', 297.</ref> [[Dess-Martin periodinane]] (DMP) offers the advantages of operational simplicity, a lack of heavy metal byproducts, and selective oxidation of complex, late-stage synthetic intermediates.<ref>{{cite journal |doi=10.1002/047084289X.rt157m.pub2|title=1,1,1-Triacetoxy-1,1-dihydro-1,2-benziodoxol-3(1H)-one|journal=Encyclopedia of Reagents for Organic Synthesis|year=2009|last1=Boeckman|first1=Robert J.|last2=George|first2=Kelly M.|isbn=978-0471936237 }}</ref> Additionally, both DMP and [[manganese dioxide]] (MnO<sub>2</sub>) can be used to oxidize allylic alcohols to the corresponding enones without allylic transposition. When allylic transpositions is desired, however, chromium(VI)-amine reagents are unrivaled.
Catalytic methods employing cheap, clean terminal oxidants in conjunction with catalytic amounts of chromium reagents produce only small amounts of metal byproducts.<ref>Muzart, J. ''Tetrahedron Lett.'', '''1987''', ''28'', 2133.</ref> However, undesired side reactions mediated by stoichiometric amounts of the terminal oxidant may occur.
| |||